Adenosine, by its reaction with specific receptors, can act as a "modulator" of synaptic activity in the central nervous system. In this role it serves to influence intracellular communication by modifying the synthesis, release, reuptake and metabolism of primary neurotransmitters. Because of its central regulatory role, adenosine influences the effects of numerous drugs of abuse on their respective target receptors, with the potential of playing a part in the processes of addiction and withdrawal. It is the overall objective of this proposal to provide crucial biochemical information about adenosine receptors that can lead to a rational approach to designing suitable drugs for the treatment of addiction to drugs of abuse. Immunological and molecular biological procedures will be used in pursuit of the following specific aims: 1. To purify the A1 adenosine receptor using a combination of affinity chromatography, lectin chromatography and the specific monoclonal antibodies; 2. To obtain partial amino acid sequences of the A1 adenosine receptor; 3. To construct cDNA libraries from tissues that express relatively high levels of the A1 adenosine receptor, e.g., rat hippocampus; 4. To screen the cDNA libraries with oligonucleotides synthesized according to the partial amino acid sequence of the A1 adenosine receptor; 5. To obtain full length cDNA that codes for the A1 adenosine receptor; 6. To express the full length cDNA in vitro and in eukaryotic cells; 7. To use the cDNA probe to investigate the distribution and expression level of the A1 adenosine receptor in various tissues and organs, in both normal and drug-related animals; 8. To use mutagenesis procedures to study structural features of the A1 receptor.